DONETSK, Ukraine--Fighting raged Sunday in the eastern Ukrainian city of Donetsk despite a request from the pro-Russian rebels there for a cease-fire to prevent a "humanitarian catastrophe."

One person was killed and 10 injured in shelling that started early Sunday morning and continued into the day, city council spokesman Maxim Rovinsky told The Associated Press.

Conditions were clearly deteriorating in Donetsk, the largest rebel stronghold in eastern Ukraine. Associated Press reporters heard 25 loud explosions in as many minutes around noon. More than 10 residential buildings, as well as a hospital and a shop, were heavily damaged by shelling overnight, and several buses caught in the crossfire were still burning Sunday morning.

At least 300,000 of Donetsk's 1 million residents have fled as violence escalates between Ukrainian government forces and pro-Russian separatists, claiming the lives of over 1,300 people since April, according to the U.N.

"This is a real war! It's impossible to live in this city, I've been sleeping in the basement for the past week," said Inna Drobyshevskaya, a 48-year-old lawyer in Donetsk.

"We don't want Novorossiya (New Russia) for this price," she added, referring to a term used by rebels to describe the parts of eastern Ukraine seeking independence from the government in Kiev.

On Saturday, rebel leader Aleksandr Zakharchenko called for a cease-fire but his request was met warily by both the Ukrainian government in Kiev and the West. Those leaders expressed concern that the move could be aimed at increasing international pressure on Ukraine to allow in a Russian aid mission. The West says that could be used as a pretext to bring Russian soldiers into Ukraine — and says 20,000 of them are massed near the Russian border with Ukraine.

Ukrainian President Petro Poroshenko and Western leaders have repeatedly accused Russia of providing arms and expertise to the rebels, something Russia denies.

Poroshenko issued a statement late Saturday saying that Ukraine was prepared to accept humanitarian assistance in eastern Ukraine. But he said the aid must come in without military assistance, pass through border checkpoints under Ukrainian control and be an international mission.

Poroshenko said he and German Chancellor Angela Merkel discussed German participation in such a mission.